Blender Cycles quickly renders animation just black
Cycles Render uses a different node set-up for the materials then Blender Render. (You can check that for both Cycles Render and Blender Render by opening the Node Editor, with 'Use Nodes' enabled) After switching to Cycles Render,  it doesn't contain the materials you have set up in Blender Render. You must make the new materials in Cycles Render yourself.